Of course, the holes don't stay 3' deep. After the tough work of digging, I fill them with a mix of wood, moss, leaves, waste paper, bones, organic debris I rake from the chicken yard, raw manure, straw, biochar, etc.
Here's my process: the first thing I did was dig a pit, then throw in some chicken-yard debris or waste paper.
Then, I dumped in sticks, pieces of logs, or, in this case, busted-up pallet wood.
After that, a generous helping of raw manure and urine-soaked straw.
Then, I gave the whole thing a good soaking with the hose.
I found it quite encouraging that a few weeks after I started on this project, Leon posted the results of his own experiment with burying phone books. I hope that this summer I will in fact grow some melons (and squash!) in the front yard. I've had problems getting the more tender plants through the hot and dry months before the summer rains kick in. I'm praying this is the answer. I've already put in 4 or 5 of these out front between the young fruit trees. I suppose at the very worst, I've simply loosened and spot-fertilized what was previously almost worthless sand.
Wish me luck.